Mines of Torsol, setting work, please critic

This description is for a story i'm making, and i'm going for dark and sinister, so I need a bit of constructive criticism, for more darkness and "Sinisteria"

Ok, here goes

The mines.
Those deep, huge, dark ugly places.
No man ever came out from the darkened tunnels. No light did shed in the cavernous, filthy vein chambers. Incessant hammering, it's all one ever heard. There were no shifts, only work till you dropped, carried off by the armpits by two Overseers.
And the accidents.
What they mined, a dark, opaque material, was no creation of the Earth. It was volatile, but not only that, it caused greed. Suffering. Death. Men who carried it secretly were lucky if they got whipped and had it taken from them. But they did whatever they could to keep it. It was the material's fault. It made them keep it. They kept it close to them, and after a while, the man changed.
He stopped talking to those closest to them. His eyes, no matter what color they were or how bright, darkened to a deep, deep shade of red. Their faces became sallow, and their bones showed through their clothing.
In the final stages, the man might be working, chipping at rock or lugging something, when he'd cry out. He'd drop to the ground, screaming, his hands at his face, clawing. After a short time, he'd collapse, breathing rapidly, spasming.
Then he'd rear up again, retch and retch and retch, and some miners swear to have seen something dark come from the mouth, and then the man would drop, dead. He'd be thrown into one of the dangerous tunnels, and his corpse would never be seen again.
After a period of ten years, a worker would be allowed out of the mines, his pockets full.
As if anyone ever survived the first two years.

Where did the "material" came from if it's not natural? An alchemical deviation? A failed alien experiment? Remnant of an ancient culture?
Where do the miners come from? What is "outside"? Is there an actual outside, or you're planning to write some sort of Kafkaesque allegory?
Work in your mines sounds more like slave labour. What is the motivation for your miners? Are they really slaves who are promised freedom just so they would endure more? No need to promise them money and "full pockets" if they are slaves!
Do you have an actual main character, or are you going for a group character ("The Miners") or maybe even the symbolic main character ("The Mine" itself)?

And a thought: cut out the gore! Red eyes and dark pukes are disgusting, but not sinister. It maybe interesting to have such details only as hear-say: things you'd expect more experienced miners would tell the young, promising ones, just to scare them a bit.

I think you should elaborate on what does this "material" do. Does it give them a vision of life outside of the mines? Does it give them special powers? The reason why I ask is because you mention that

Men who carried it secretly were lucky if they got whipped and had it taken from them. But they did whatever they could to keep it

Click to expand...

so the material must be valuable to Overseers.

Also you should mention the amount of miners in the mines. Because only two Overseers seems small for the tunnels in my opinion